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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<script>
    var word;
    document.write(typeof word+'<br/>')//未给Word赋值
    var name = 'Lisa';
    document.write(typeof name+'<br/>')//因为名字是字符串
    var age=15; age=age + "" ; 
    document.write(typeof age+'<br/>')//数值跟字符串连接在一起就是字符串类型
    var a=5;b='4';a = a+b ; 
    document.write(typeof a+'<br/>')//数值跟字符串连接在一起就是字符串类型
    var x=10;y='10'; var flag = x == y; 
    document.write(typeof flag)//有判断所以是boolean
</script>
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